The invention relates generally to non-invasive imaging such as single photon emission computed tomography (SPECT) imaging. More particularly, the invention relates to cross-slit collimators for use in non-invasive imaging.
SPECT is used for a wide variety of imaging applications, such as medical imaging. In general, SPECT systems are imaging systems that are configured to generate an image based upon the impact of photons (generated by a nuclear decay event) against a gamma-ray detector. In medical and research contexts, these detected photons may be processed to formulate an image of organs or tissues beneath the skin.
To produce an image, one or more detector assemblies may be rotated around a subject. Detector assemblies are typically comprised of a plurality of structures working together to receive and process the incoming photons. For instance, the detector assembly may utilize a scintillator assembly (e.g., large sodium iodide scintillator plates) to convert the photons into light for detection by an optical sensor. This scintillator assembly may be coupled by a light guide to multiple photomultiplier tubes (PMTs) or other light sensors that convert the light from the scintillator assembly into an electric signal. In addition to the scintillator assembly-PMT combination, pixilated solid-state direct conversion detectors (e.g., CZT) may also be used to generate electric signals from the impact of the photons. This electric signal can be easily transferred, converted, and processed by electronic modules in a data acquisition module to facilitate viewing and manipulation by clinicians.
Typically, SPECT systems further include a collimator assembly that may be attached to the front of the gamma-ray detector. In general, the collimator assembly is designed to absorb photons such that only photons traveling in certain directions impact the detector assembly. For example, multi-hole collimators comprised of multiple, small-diameter channels separated by lead septa have been used. With these multi-hole collimators, photons that are not traveling through the channels in a direction generally parallel to the lead septa are absorbed. In addition, while parallel-hole collimators are typically used, collimators also may have converging holes for image magnification or diverging holes for minifying the image. For improved resolution, a pinhole collimator may be used. By way of example, an improved image resolution may be obtained with a pinhole collimator, e.g., if the subject is closer to the pinhole than the pinhole is to the gamma-ray detector.
While current SPECT systems have been used successfully, these systems have a number of disadvantages. For instance, rotation of the gamma-ray detectors along with the corresponding collimator assemblies around the subject typically requires large and expensive positioning systems capable of rotating the equipment with the needed precision. In addition, extended examination times are typically required because the detector assemblies must be rotated around the subject to obtain images from multiple angles around the subject. Moreover, current systems also do not provide the desired resolution and sensitivity. By way of example, the sensitivity of SPECT systems with multi-hole collimators may be reduced because only photons traveling in a direction generally parallel to the axis of the holes pass through the collimator. For similar reasons, SPECT systems with multi-hole collimators also may not provide the desired positional resolution.
Accordingly, it would be desirable to provide an imaging system with improved positional resolution and sensitivity while also having reduced examination times and simpler positioning systems.